Currently, many pressure-sensitive adhesive tapes and other pressure-sensitive adhesive-coated articles have a release liner applied to the adhesive during or following manufacture. For example, the release liner can serve as a carrier for a pressure sensitive adhesive transfer tape or a double-coated tape, both of which are tacky on both sides of the tape. The adhesive tape on a release liner is typically supplied on a convolutely wound roll, and then unwound and laminated to an article or substrate. The release liner is typically left in place while the article is converted, packaged, and shipped to ultimate users, and in many instances is left in place until the article is bonded to and adhered to another substrate with the pressure-sensitive adhesive. Release liners are used for one or more of a number of purposes, including, for example, preventing contamination of the adhesive layer, facilitating handling of the adhesive-coated article (e.g., by providing support thereto as well as covering the adhesive), identifying the articles to which they are applied, etc.
The type of adhesive is typically matched to the type of release liner. For example, state-of-the-art release liners for acrylic pressure-sensitive tapes are polyethylene or polypropylene films. These films have been successfully used for acrylic pressure-sensitive adhesives for many years because they do not require a separate coating (e.g. silicones) to provide a release surface. Silicone-coated polyester release liners are also well-known in the art.
Conventional polyolefin-based or polyester release liners that function well at ambient temperatures are, however, often unsuitable for use in manufacturing processes that involve heating and cooling a substrate after application of an adhesive tape but before removal of the release liner. For example, during the painting process, painted thermoplastic automobile parts are typically exposed to temperatures of about 250° F. or higher for extended periods of time to cure the paint and then cooled. It is often desirable to apply an adhesive tape with a release liner to an unpainted substrate, paint the substrate and cure the paint at high temperature, then remove the release liner after cooling. Polyethylene release liners, however, cannot withstand high temperatures used in paint curing ovens and can melt, shrink or buckle during procedures that involve heating and cooling. Silicone-coated polyester liners can withstand high temperatures, but are also unsuitable for applications that involve thermal cycling because they do not expand and contract at the same rate as thermoplastic polyolefin substrates when heated and cooled, and the polyester liners tend to pull away from the ends of the adhesive tape upon heating or buckle upon subsequent cooling.
What is needed in the industry is a release liner for pressure sensitive adhesives, particularly for acrylic foam tapes, that is suitable for use in manufacturing applications that involve heating and cooling of a substrate.